From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Eric W. Biederman" Date: Tue, 03 May 2022 19:36:55 +0000 Subject: Re: [PATCH v2 06/12] ptrace: Reimplement PTRACE_KILL by always sending SIGKILL Message-Id: <87y1zio1bc.fsf@email.froward.int.ebiederm.org> List-Id: References: <87k0b7v9yk.fsf_-_@email.froward.int.ebiederm.org> <20220429214837.386518-6-ebiederm@xmission.com> <20220502143750.GC17276@redhat.com> In-Reply-To: <20220502143750.GC17276@redhat.com> (Oleg Nesterov's message of "Mon, 2 May 2022 16:37:51 +0200") MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, rjw@rjwysocki.net, mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon , tj@kernel.org, linux-pm@vger.kernel.org, Peter Zijlstra , Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn , linux-ia64@vger.kernel.org, stable@vger.kernel.org, Al Viro Oleg Nesterov writes: > On 04/29, Eric W. Biederman wrote: >> >> Call send_sig_info in PTRACE_KILL instead of ptrace_resume. Calling >> ptrace_resume is not safe to call if the task has not been stopped >> with ptrace_freeze_traced. > > Oh, I was never, never able to understand why do we have PTRACE_KILL > and what should it actually do. > > I suggested many times to simply remove it but OK, we probably can't > do this. I thought I remembered you suggesting fixing it in some other way. I took at quick look in codesearch.debian.net and PTRACE_KILL is definitely in use. I find uses in gcc-10, firefox-esr_91.8, llvm_toolchain, qtwebengine. At which point I stopped looking. >> --- a/kernel/ptrace.c >> +++ b/kernel/ptrace.c >> @@ -1238,7 +1238,7 @@ int ptrace_request(struct task_struct *child, long request, >> case PTRACE_KILL: >> if (child->exit_state) /* already dead */ >> return 0; >> - return ptrace_resume(child, request, SIGKILL); >> + return send_sig_info(SIGKILL, SEND_SIG_NOINFO, child); > > Note that currently ptrace(PTRACE_KILL) can never fail (yes, yes, it > is unsafe), but send_sig_info() can. If we do not remove PTRACE_KILL, > then I'd suggest > > case PTRACE_KILL: > if (!child->exit_state) > send_sig_info(SIGKILL); > return 0; > > to make this change a bit more compatible. Quite. The only failure I can find from send_sig_info is if lock_task_sighand fails and PTRACE_KILL is deliberately ignoring errors when the target task has exited. case PTRACE_KILL: send_sig_info(SIGKILL); return 0; I think that should suffice. > Also, please remove the note about PTRACE_KILL in > set_task_blockstep(). Good catch, thank you. Eric